Process for producing hydrocyanic acid



J5 FORM/:mae

HEATER IN VEN TOR.

W. COOPEY PROCESS FOR PRODUCING HYDROCYANIC ACID Filed Oct. 9, 1945 .70 Il CN SGEI/BBEK Dec. 12, 1950 16 THEmo coz/PLE WELL Patented Dec. 12, 1950 UNITED STATES PATENT OFFICE PROCESS FOR PRODUCING HYDRO- CYANIC ACID Application October 9, 1945, Serial No. 621,37 3

. 2. Claims.

This invention relates tc a process for the preparation of hydrocyanic acid and more particularly to process for its preparation from formamide and to apparatus therefor,

In catalytic reactions which are highly endothermic and especially those conducted` at high temperature levels, such as the catalytic conversion of formamide to hydrocyanic acid, it is essential that eflicient heat exchange means be provided in order that sufficient heat flows into the catalyst to maintain the reaction at temperature. Moreover, in the formamide to hydrocyanic acid reaction many precautions must be taken in bringing the formamide up to the temperature of conversion which is conducted with the formamide in the vapor phase. Considerable diliiculty has heretofore been encountered in vaporizing formamide because it decomposes rapidly at its boiling :point 192 C.-195 C. to carbon monoxide and ammonia. To avoid decomposition it has been proposed heretofore to vaporize the formamide at reduced pressure, to vaporize it from heated surfaces and to flash vaporize it. Such proposals require more or less elaborate apparatus necessitating careful control which have not been entirely satisfactory due to decomposition, inability to provide sufcient `uniform heat distribution, plugging of apparatus and feed linesand other operating difculties.

An object of the present invention is to provide a process for the preparation of hydrocyanic acid. Another object is to provide an economical process for vaporizing formamide. A further object is to provide a process for efliciently and 4catalytically converting formamide to hydrocyanic acid by a vapor phase process. Other objects and advantages of the invention will hereinafter appear.

The catalytic conversion in the vapor phase of formamide to hydrocyanic acid is well known, the reaction taking place in the vapor phase at a temperature between 400 and 650 C. usually under atmospheric pressure in the presence of suitable catalysts for the reaction such, of ex.- ample, as chromium, aluminum and/or manganese metal filings, activated charcoal, alumina, pumioe and other metals and their oxides. `The invention of this case is not directed `to conditions oi temperature, pressure or catalysts, which are well known, but to the manner of conducting the reaction.

The accompanying drawing which is a diagrammatic cross sectional elevation through the center of a preferred embodiment of the invention illustrates an apparatus in which forniamide can be efficiently and economically hydrogenated to hydrocyanic acid. Referring to Fig. 1 of the drawing, I is a metal support from which two reaction vessels `2 and 3, are suspended, vessel 2 being a vaporizer for formamide, vessel 3 a catalytic reaction converter, the vessels being disposed in insulating jackets 4 and 5 supported `on a metal support IA.

inasmuch as the catalyitc conversion of formarnide to hydrocyanic acid is a high temperature reaction requiring the addition of heat, the vessels are l.encased in ninsulation 30 and heat resisting brick walls 4, encased inV steel 5.

Directing our attention to the formamide vaporizer 2, this vessel is a metallic tube, of for example aluminum or its alloys or other metal having no effect Aon the vapors, flanged at top and bottom, the upper flange 8 supporting the tube 2 and resting `on Support I. The tube 2 is loosely fitted into the upper furnace wall cap 4a, which permits expansion and contraction .during the heating and cooling operation. The upper flan-ge ,8 of tube 2 is also bolted to a liquid distributing mechanism through flange 9, said liquid distributing mechanism ,comprising a power driven pulley Il), bearings II and shaft IIa. An aluminum ,distributor I2 which is cup shaped and closed at the bottom is xed to shaft I-Ia Pipe i3 extends into `the top of distributor I2. Centrally supported within the vaporizer tube 2 is a tube I4 closed at the top and constructed of alloy steel which provides an annulus between its outer wall and the inner wall of the Atube 24, L,see Fig. 2. Tube I4 is supported by structural members I5 which `centers tube I4 in the vapor,- izer tube 2. A thermocouple well I6 is provided within tube I4.

`The catalyst reaction tube 3, constructed ofl any `suitable metal such, for example, as copper or stainless steel with an inner surface of cop-f per, is located in a separate furnace adjacent the 4furnace of the vaporizer tube 2. The cata- -lyst tube 3 is supported on flanges 8 and 9 in a manner simi-lar to the support of the vaporizer `tube 2. The upperilange 8 of catalyst tube 3 .is .bolted ,to flange 9 which supports an annular header Il heading into tube I8. Flanges 8 and 9 of Ythe catalyst tube likewise support a copper core tube or cylinder .i9 having the same axis as the `catalyst ,tube 3, tube I9 is closed at the :top and bottom. Tube AIl) does ,not reach tothe bottom of the catalyst tube `3,. Expansion and contraction of the catalyst tube 3 is compensated for by movement through the furnace wall cap Vla while heat expansion and contraction of the tube i 9 is compensated for by movement into the catalyst tube 3. The annulus between the outer wall of tube iii and the inner wall of catalyst tube 3 is packed with a suitable catalyst for the lated electrical resistance heating elements 23 embedded in heat insulation which fills the annulus between the outer walls respectively of the vaporizer tube 2 and catalyst tube'a and the inner walls of the furnace. Fig, 2, a. cross section taken at AA, shows these annuli. The lower portion of the vaporizer tube 2 is used as a superheater of the vaporized formamide and additional heating elements are provided aboutV the tube at this position to effect this result. Tube 2| interconnecting the vaporizer and catalyst tubes, is provided with an electrical heating element 2li and a drain 25. A steam heated preheater the use oi which is optional, may be used to preheat the iormamide as it hows through pipe 13 into the rotating distributor cupi2.

The converter and vaporizer operate in this manner. Liquid formamide is continuously introduced into pipe i3, ows into the preheater 2S wherein its temperature is raised to between 135 and 140 C. The temperature of the formamide should not exceed 140 C. for at such temperatures it decompcses to carbon monoxide and ammonia and these gases inter alia produce erratic fluctuations in ow through the apparatus which are detrimental to Veiicient operation. The preheated formamide flows from pipe i3 into the rotating distributor i2 which is provided with'two diametrically opposed holes in its peripher Iza,V

one of which is shown. As the distributor spins at a speed in the order of 200 R. P. M., the liquid formamide is discharged through the small holes lZa against the inner walls of the vaporizer tube 2 forming a liquid film which ows downwardly. The tube is heated sulciently to vaporize rapidly the formamide and as the vapors are forced downward they are superheated to a temperature of between 400 and 500 C. at which temperature they pass from the bottom of the Vaporizer. The thus vaporizedrand superheated formamide passes through the conduit 2i over the heating element 24 through the screen 29 and into the catalyst tube wherein it comes in direct contact with the catalyst 2.7.k If desired copper rings, silica 'or other material may be placed immediately above screen 29 to provide additional preheat for the vapors just prior to Vthe reaction. 'Due to the high endothermicity of the reaction heat is provided not only from the electric heating elements- 23, surrounding the catalyst tube 3, but also from `When the above method and apparatus are operated with formamide, preheated to a temperature of about 135 C. and vaporized in a vaporizer tube to a temperature between 420 and (fifi Y heating elements located within the .core tube l 9. By these multiple means an adequate amount of heat can be passed into the catalyst thereby replacing theA large amount of heat lost during the course of the reaction. The gases pass upwardly through the annular catalyst space 21 into the annular header i7 and out through the tube I8 to a scrubber not shown,Y wherein the hydrocyanic acid" is separated by any suitable means from the other gases of the reaction,

Y4:60" C. with converter temperatures at about 50G-600 C. employing a manganese metal catalyst approximately a yield of hydrocyanic acid can be continuously maintained.

It is apparent from the above description that the apparatus and method described herein specifically for the conversion of formamide to hydrocyanic acid are likewise applicable for use in other organic reactions of an endothermic nature and especially for use in Such reactions Vin which it is difficult to vaporize the reactants i without undue decomposition.

I claim:

1. In a process for the catalytic conversion of formamide to hydro'cyanic acid; the steps which comprise preheating liquid formamide to a temperature between and 140 C., forming the preheated liquid in the shape of a falling film of annular cross section, externally and internally heating the nlm while passing it downwardly through a'zone of vaporization, Vaporizing the liquid andV superheating the resulting vapor while maintaining the'annular shape of the fluids, passing the vapors immediately after `being superheated, and without substantial loss of superheat, up and through a heated'catalyst zone of annular cross section wherein the formainide is pyrolyzed to hydrocyanic acid inthe presence of a manganese catalyst at a temperature between 400 and 650 C. and supplying heat to the reaction by heat now into the zone through the outer and inner concentric boundaries thereof.

2.V In a process for the catalytic conversion of form-amide to hydrocyanic acid, the steps which comprise preheating liquid ormarnide to a temperature between 135 and 140 C., forming the preheated liquid by spraying in the shape of V'a falling lm of annular cross section, exterzone of annular cross section wherein the form- Y amide is pyrolyzed in the presence ci a manganese catalyst to hydrocyanic acid and supply- Y f, ing heat to the reaction by heat flow into the zone through outerv and inner concentric boundaries of the zone. Y

Y WALTER COOPEY.

- REFERENCES CITED The following references are of record inthe iile of this patent:

UNITED, sfra'rnsY PATEN'rs Broderson Aug. 27, 1940 

1. IN A PROCESS FOR TEH CATALYTIC CONVERSION OF FORMAMIDE TO HYDROCYANIC ACID, THE STEPS WHICH COMPRISE PREHEATING LIQUID FORMAMIDE TO A TEMPERATURE BETWEEN 135 AND 140 DEGREES C., FORMING THE PREHEATED LIQUID IN THE SHAPE OF A FALLING FILM OF ANNULAR CROSS SECTION, EXTERNALLY AND INTERNALLY HEATING THE FILM WHILE PASSING IT DOWNWARDLY THROUGH A ZONE OF VAPORIZATION, VAPORIZING THE LIQUID AND SUPERHEATING THE RESULTING VAPOR WHILE MAINTAINING THE ANNULAR SHAPE OF THE FLUIDS, PASSING THE VAPORS IMMEDIATELY AFTER BEING SUPERHEATED,A DN WITHOUT SUBSTANTIAL LOSS OF SUPERHEAT, UP AND THROUGH A HEATED CATALYST ZONE OF ANNULAR CROSS SECTION WHEREIN THE FORMAMIDE IS PYROLYZED TO HYDROCYANIC ACID IN THE PRESSENCE OF A MANGANESE CATALYST AT A TEMPERTURE BETWEEN 400 AND 650 DEGREES C. AND SUPPLYING HEAT TO THE REACTION BY HEAT FLOW INTO THE ZONE THROUGH THE OUTER AND INNER CONCENTRIC BOUNDARIES THEREOF. 